STIHL 420 Concrete Saw Manual

The STIHL 420 Concrete Saw is a powerful, professional-grade cutting tool designed for heavy-duty concrete, asphalt, and masonry work. It features a high-performance engine, diamond cutting blades, water feed system for dust suppression, ergonomic handles, and safety features including a throttle lockout and chain brake. Below are key sections for safety, features, assembly, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: High-torque 2-stroke engine, Diamond cutting blade, Water feed connection, Throttle trigger with lockout, Front handle with vibration damping, Rear handle with grip, Chain brake lever, Fuel tank, Blade guard.

Assembly & Installation

Unpack and inspect all parts. Assemble on a clean, stable surface.

1. Attach the cutting blade: Ensure saw is off. Remove blade guard bolt, place blade on spindle, secure with flange and bolt (tighten clockwise).
2. Install the blade guard: Align guard with mounting points and secure with provided screws.
3. Connect water hose: Attach supplied hose to water inlet on saw. Connect other end to water source.
4. Fuel mixture: Prepare correct gasoline and 2-stroke oil mix as specified. Fill fuel tank.

WARNING! Always wear cut-resistant gloves when handling the blade. Ensure all fasteners are tight before operation.

First-Time Operation

Perform pre-operation checks before starting.

1. Check fuel level: Ensure adequate fuel/oil mix.
2. Inspect blade: Verify blade is secure and undamaged.
3. Water supply: Turn on water to ensure flow to blade.
4. Start the engine: Set on flat surface. Engage throttle lockout, pull starter cord firmly.
5. Test controls: Verify throttle response and chain brake function.

CAUTION! Never operate without water supply for dust suppression. Keep bystanders at a safe distance.

Specifications

• Engine Type: 2-stroke, single cylinder
• Displacement: 64.8 cc
• Power Output: 4.2 kW
• Max Blade Diameter: 14 inches (355 mm)
• Max Cutting Depth: 5.1 inches (130 mm)
• Fuel Capacity: 1.3 liters
• Weight (without blade): 11.2 kg
• Sound Power Level: 112 dB(A)
• Vibration Level: Front/Back handle: 5.2/6.1 m/s²

Controls and Settings

Main controls located on handles and body.

Front Handle: Throttle trigger, Throttle lockout lever, Chain brake lever.

Rear Handle: Main grip, Starter grip.

Body: On/Off switch, Choke lever, Fuel tank cap, Water inlet, Depth adjustment knob.

Operation: Squeeze throttle lockout and trigger to increase engine speed. Push chain brake lever forward to engage brake (stops blade). Use depth adjustment to set cutting depth before starting cut.

Connecting Water Supply

Water is essential for cooling the blade and suppressing hazardous dust.

1. Turn off saw and water source.
2. Connect hose to water inlet fitting on saw (ensure seal is tight).
3. Connect other end of hose to tap or water pump.
4. Turn water on and check for leaks and adequate flow at blade.
5. Adjust flow if necessary using regulator on hose (if equipped).

Tip: Always use clean water to prevent clogging of the water jets.

Cutting Techniques

For straight, controlled cuts in concrete and asphalt.

1. Mark cut line clearly on surface.
2. Set desired cutting depth using adjustment knob.
3. Start engine and allow to reach operating speed.
4. Begin cut at edge of material, lowering blade gradually into cut line.
5. Use steady, forward pressure—do not force the saw.
6. For deep cuts, make multiple passes, increasing depth incrementally.
7. Keep water flowing throughout the entire cut.
8. At end of cut, release throttle and allow blade to stop before lifting.

WARNING! Never cut without water. Avoid twisting or bending the blade during cut. Beware of rebound (kickback).

Safety Features

Chain Brake: Manually activated lever stops blade rotation instantly. Throttle Lockout: Must be depressed before throttle can be engaged, preventing accidental acceleration. Blade Guard: Covers upper portion of blade. Vibration Damping: Reduces transmitted vibration to operator's hands.

Care & Maintenance

Regular maintenance ensures performance and longevity.

1. After each use: Clean exterior with damp cloth. Flush water system.
2. Daily: Check blade for damage/wear. Inspect all fasteners for tightness.
3. Weekly: Clean air filter. Check fuel lines for cracks.
4. Monthly: Clean spark arrestor in muffler. Check/replace spark plug.
5. Blade Care: Keep diamond segments clean and sharp. Replace when worn.

CAUTION! Always disconnect spark plug wire before performing maintenance. Use only STIHL recommended parts and lubricants.

Regulatory Information

Complies with relevant machinery safety directives. Emissions comply with EPA Phase 2 and EU Stage II regulations. The saw incorporates safety standards for hand-held concrete cutters. For genuine parts, accessories, and service, contact an authorized STIHL dealer. © STIHL Incorporated. STIHL is a registered trademark. Operator's manual part number: 0000-970-8501.

Troubleshooting

Service: For repairs beyond basic maintenance, contact an authorized STIHL service dealer.

Support: Visit www.stihlusa.com or call 1-800-467-8445 for dealer locations.